A technique that connects a switching element and a diode in parallel, and utilizes the diode in a flyback diode is known (e.g. Japanese Patent Application Publication No. 2002-164503). When a current flowing in a coil (e.g., reactor or motor) is turned on or off by the switching element, electromotive force is generated in the coil. A current generated by the electromotive force flows in the flyback diode. Other than a PiN diode that uses a Si substrate (referred in this description as SiPiND), a Schottky-barrier diode that uses a SiC substrate (referred in this description as SiCSBD) is known. When a SiCSBD is used in the flyback diode, a reverse recovery current can be suppressed and a loss can further be reduced than the SiPiND. Further, the SiCSBD has a higher resistance against breakage than the SiPiND, and can be used in a higher current density than the SiPiND.
A diode provided with a front surface electrode and a rear surface electrode, and that is used by connecting these electrodes to a conductor via solder layers is known. When a current flows in the solder layers, a phenomenon in which substances configuring the solder layers move and a quality of the solder layers deteriorates (this is called electro migration, referred in this description as EM) progresses. The EM has a faster progression rate with larger current densities, and has a faster progression rate with higher temperatures of the solder layers.
In a case of configuring a flyback diode by bonding solder layers to a front surface electrode and a rear surface electrode of the SiCSBD, EM tends to progress within the solder layers. As aforementioned, the SiCSBD can be used in a high current density. The current density that does not become problematic in the SiCSBD results in a current density by which EM progresses in the solder layers.
If a substrate area of the SiCSBD is made large, a difference in areas of solder layers for the front surface electrode and the rear surface electrode becomes large, and the current density can be reduced and a progression rate of the EM taking place in the solder layers can be reduced.
However, a SiC substrate contains a large number of crystal defects, and if the substrate area is increased, yield for obtaining the SiCSBD decreases and manufacturing cost of the SiCSBD is increased. Accordingly, there is a demand for utilizing the SiCSBD, which can be manufactured with satisfactory yield and small substrate area, and used in a large current density.